Similar with specified size

[rveltz]

Hi,

Is there a way to make this work for Array and Static Arrays?

Thank you

v1 = MVector(1, 2, 3)
similar(v1,4)

[andyferris]

similar(v1, Size(4)) is the current approach.

With constant propagation in Julia v1.0 we could potentially do this automatically, but then it would be difficult to get a dynamically sized array...

[fgasdia]

I'm interested in the same (giordano/PolynomialRoots.jl#9). The problem with Size() of course is that it requires a package to import StaticArrays when we really just want to parameterize on a user supplied type, be it an Array or SArray.

[rveltz]

If I define

similar(v::MVector,s::Int) = similar(v,Size(s))

is it likely to break your package somewhere?

[andyferris]

Potentially? I'm not 100% sure.

The problem as I see it is that sometimes generic code might expect to call similar(v::AbstractVector, i::Int) where i can't possibly be known to the compiler. In this case emitting a static array could slow down the resulting code drastically, which is a bad result. Requiring the use of Size is not very ergonomic, which isn't fantastic either, but it does has the benefit of giving the programmer control.

I'm not sure what the endgame here is. We could maybe ask to be able to dispatch or branch on "constness" - but I strongly suspect the compiler people would say something like "the problem of determining whether any given variable is found to be constant or not is undecidable (or undefined, or at the very least frequently changing as the compiler evolves) and we don't want this to affect program behavior". Anyone have thoughts on the best way to proceed?

[c42f]

@EP-Guy ultimately we may require some traits like Size in Base to solve that dependency problem.

Generally, I don't know what we can do about this for the reasons described by Andy. Would probably need to be part of a larger carefully considered design iteration.